## Calculus with Applications (10th Edition)

$D(q)=-0.5q+72.50$
A linear function will have the form $D(q)=p=mq+b$ The graph contains points ( demanded number of pills, price). Using the points (50, 47.50) and (80, 32.50), we find the slope: $m=\displaystyle \frac{47.50-32.50}{50-80} =\displaystyle \frac{15}{-30}=\frac{-1}{2}=-0.5$. The point=slope form: $p-47.50=-0.5(q-50)$ $p-47.50=-0.5q+25\qquad/+47.50$ $p=-0.5q+72.50$ or $D(q)=-0.5q+72.50$